A major goal of this grant was to perform a prospective randomized study of two anti-thymocyte globulin (ATG) preparations differing in immunosuppressive potency as determined by primate skin graft testing. Renal transplant patients were assigned at the time of transplantation into two groups by the Teves minimization technique to eliminate significant differences in concomitant variates between the 2 groups for the following variables: age, sex, degree of pre-sensitization, primary vs. secondary transplant, and HLA A and B locus matching. Clinicians managing the patients post-transplant were unaware of the patient ATG assignment. To date 71 patients have been entered in the study with a mean follow-up of over 1 year. Using actual analysis at one year and actuarial analysis at two years post-transplant, there is a significant difference in allograft survival between the two groups. When the code was broken, it was determined that the group with superior results had received high potency ATG. The main difference in the graft survival curves appeared to have occurred in the first three months post-transplant. Monitoring of T cells and reactivity indicated that high potency ATG lowered T cell levels and reactivity were associated with a marked diminution in early acute rejection activity. BIBLIOGRAPHIC REFERENCES: Thomas, J., Thomas, F. and Lee, H.M.: Immunological monitoring of long surviving renal transplant recipients. Surgery 81:125-131, 1977. Thomas, J., Thomas F. and Lee, H.M.: Studies of lymphocyte-dependent antibody in chronic renal allograft rejection. Transplant. Proc. 9:65-68, 1977.